Colossal Explosion Challenges Our Understanding of Gamma-Ray Bursts

International Gemini Observatory uncovers surprising evidence of colliding neutron stars after probing aftermath of gamma-ray burst.

While investigating the aftermath of a long gamma-ray burst (GRB), two independent teams of astronomers using a host of telescopes in space and on Earth have uncovered the unexpected hallmarks of a kilonova. This is the colossal explosion triggered by colliding neutron stars. This discovery challenges the prevailing theory that long GRBs exclusively come from supernovae, the end-of-life explosions of massive stars.

Gamma-ray bursts (GRBs) are the most energetic explosions in the Universe. They come in two varieties, long and short. Long GRBs, which last a couple of seconds to one minute, form when a star at least 10 times the mass of our Sun explodes as a supernova. Short GRBs, which last less than two seconds, occur when two compact objects, like two neutron stars or a neutron star and a black hole, collide to form a kilonova.

While observing the aftermath of a long GRB detected in 2021, two independent teams of astronomers found the surprising signs of a neutron-star merger rather than the expected signal of a supernova. This surprising result marks the first time that a kilonova has been associated with a long GRB and challenges our understanding of these phenomenally powerful explosions.

This Gemini North image, superimposed on an image taken with the Hubble Space Telescope, shows the telltale near-infrared afterglow of a kilonova produced by a long GRB (GRB 211211A). This discovery challenges the prevailing theory that long GRBs exclusively come from supernovae, the end-of-life explosions of massive stars. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Zamani; NASA/ESA

The first team to announce this discovery was led by Jillian Rastinejad, a PhD student at Northwestern University. Rastinejad and her colleagues made this startling discovery with the help of the Gemini North telescope on Hawai‘i, part of the International Gemini Observatory, which is operated by NSF’s NOIRLab. The Gemini North observations revealed a telltale near-infrared afterglow on the exact location of the GRB, offering the primary compelling proof of a kilonova related to this occasion.^[1] Rastinejad’s crew promptly reported their Gemini detection in a Gamma-ray Coordinates Network (GCN) Circular.

Astronomers all over the world have been first alerted to this burst, named GRB 211211A, when a robust flash of gamma rays was picked up by NASA’s Neil Gehrels Swift Observatory and Fermi Gamma-ray Space Telescope. Initial observations revealed that the GRB was uncommonly close by, a mere one billion light-years from Earth.

Interview with Eleonora Troja, an astronomer on the University of Rome Tor Vergata, who studied the afterglow of the GRB utilizing a collection of observations, together with the Gemini South telescope in Chile, and independently concluded that the lengthy GRB got here from a kilonova.

Most GRBs originate within the distant, early Universe. Typically, these objects are so historic and much flung that their mild would have needed to journey for greater than six billion years to achieve Earth. Light from the most-distant GRB ever recorded traveled for practically 13 billion years earlier than being detected right here on Earth.^[2] The relative proximity of this newly found GRB enabled astronomers to make remarkably detailed follow-up research with quite a lot of ground- and space-based telescopes.

“Astronomers usually investigate short GRBs when hunting for kilonovae,” stated Rastinejad. “We were drawn to this longer-duration burst because it was so close that we could study it in detail. Its gamma rays also resembled those of a previous, mysterious supernova-less long GRB.”

A novel observational signature of kilonovae is their brightness at near-infrared wavelengths in comparison with their brightness in seen mild. This distinction in brightness is because of the heavy components ejected by the kilonova, which successfully block seen mild however permit the longer-wavelength infrared mild to go unimpeded. Observing within the near-infrared, nevertheless, is technically difficult and solely a handful of telescopes on Earth, like the dual Gemini telescopes, are delicate sufficient to detect this kilonova at these wavelengths.

Jillian Rastinejad, a PhD pupil at Northwestern University, and her colleagues used the Gemini North telescope to disclose a telltale near-infrared afterglow on the exact location of the GRB, offering the primary compelling proof of a kilonova related to this occasion.

“Thanks to its sensitivity and our rapid-response, Gemini was the first to detect this kilonova in the near-infrared, convincing us that we were observing a neutron-star merger,” stated Rastinejad. “Gemini’s nimble capabilities and variety of instruments let us tailor each night’s observing plan based on the previous night’s results, allowing us to make the most of every minute that our target was observable.”

Another crew, led by Eleonora Troja, an astronomer on the University of Rome Tor Vergata, independently studied the afterglow utilizing a unique collection of observations, together with the Gemini South telescope in Chile,^[3] and independently concluded that the lengthy GRB got here from a kilonova.

”We have been capable of observe this occasion solely as a result of it was so near us,” stated Troja. “It is very rare that we observe such powerful explosions in our cosmic backyard, and every time we do we learn about the most extreme objects in the Universe.”

The indisputable fact that two completely different groups of scientists working with unbiased datasets each arrived on the identical conclusion in regards to the kilonova nature of this GRB supplies confidence on this interpretation.

“The kilonova interpretation was so far off from everything we knew about long GRBs that we could not believe our own eyes and spent months testing all the other possibilities,” stated Troja. “It is only after ruling out everything else that we realized our decade-long paradigm had to be revised.”

As nicely as contributing to our understanding of kilonovae and GRBs, this discovery supplies astronomers with a brand new method to examine the formation of gold and different heavy components within the Universe. The excessive bodily situations in kilonovae produce heavy components corresponding to gold, platinum, and thorium. Astronomers can now establish the websites which can be creating heavy components by looking for the signature of a kilonova following a long-duration gamma-ray burst.

“This discovery is a clear reminder that the Universe is never fully figured out,” stated Rastinejad. “Astronomers often take it for granted that the origins of GRBs can be identified by how long the GRBs are, but this discovery shows us there’s still much more to understand about these amazing events.”

“NSF congratulates the science teams for this new and exciting discovery, opening a new window onto cosmic evolution,” stated National Science Foundation Director Sethuraman Panchanathan. “The International Gemini Observatory continues to deliver powerful and nimble resources open to the whole scientific community through innovation and partnership.”

For extra on this analysis, see Undetected Hybrid Neutron-Star Merger Event Revealed by Unusual Gamma-Ray Burst.

The International Gemini Observatory is operated by a partnership of six nations, together with the United States by way of the National Science Foundation, Canada by way of the National Research Council of Canada, Chile by way of the Agencia Nacional de Investigación y Desarrollo, Brazil by way of the Ministério da Ciência, Tecnologia e Inovações, Argentina by way of the Ministerio de Ciencia, Tecnología e Innovación, and Korea by way of the Korea Astronomy and Space Science Institute. These Participants and the University of Hawaii, which has common entry to Gemini, every preserve a National Gemini Office to help their native customers.

Notes

1. Rastinejad and her colleagues made preliminary follow-up observations of the burst utilizing the Nordic Optical Telescope. Following the essential Gemini North observations, they continued their observations of the fading kilonova with the Karl G. Jansky Very Large Array, the Calar Alto Observatory, and the MMT Observatory, and obtained later observations with the Large Binocular Telescope, the W. M. Keck Observatory, the Gran Telescopio Canarias, and the NASA/ESA Hubble Space Telescope.
2. Light that has traveled nearly 13 billion years to reach Earth would have a redshift (z) of about 7. Due to the accelerating expansion of the Universe, that would roughly equate to a distance of 24.5 billion light-years today. When talking about large redshifts, those greater than 1, and cosmically distant objects, it is more accurate to state how many billions of years the light has traveled rather than a distance in light-years.
3. Troja and her colleagues initially observed the afterglow of this event with the Devasthal Optical Telescope, the Multicolor Imaging Telescopes for Survey and Monstrous Explosions, and the Calar Alto Observatory. They obtained observations of the host galaxy with the NASA/ESA Hubble Space Telescope.

References:

“A kilonova following a long-duration gamma-ray burst at 350 Mpc” by Jillian C. Rastinejad, Benjamin P. Gompertz, Andrew J. Levan, Wen-fai Fong, Matt Nicholl, Gavin P. Lamb, Daniele B. Malesani, Anya E. Nugent, Samantha R. Oates, Nial R. Tanvir, Antonio de Ugarte Postigo, Charles D. Kilpatrick, Christopher J. Moore, Brian D. Metzger, Maria Edvige Ravasio, Andrea Rossi, Genevieve Schroeder, Jacob Jencson, David J. Sand, Nathan Smith, José Feliciano Agüí Fernández, Edo Berger, Peter K. Blanchard, Ryan Chornock, Bethany E. Cobb, Massimiliano De Pasquale, Johan P. U. Fynbo, Luca Izzo, D. Alexander Kann, Tanmoy Laskar, Ester Marini, Kerry Paterson, Alicia Rouco Escorial, Huei M. Sears and Christina C. Thöne, 7 December 2022, Nature.
DOI: 10.1038/s41586-022-05390-w

“A nearby long gamma-ray burst from a merger of compact objects” by E. Troja, C. L. Fryer, B. O’Connor, G. Ryan, S. Dichiara, A. Kumar, N. Ito, R. Gupta, R. Wollaeger, J. P. Norris, N. Kawai, N. Butler, A. Aryan, K. Misra, R. Hosokawa, K. L. Murata, M. Niwano, S. B. Pandey, A. Kutyrev, H. J. van Eerten, E. A. Chase, Y.-D. Hu, M. D. Caballero-Garcia, A. J. Castro-Tira, 7 December 2022, Nature.
DOI: 10.1038/s41586-022-05327-3